The present invention relates to an eyeglass lens grinding apparatus for grinding the periphery of an eyeglass lens.
An eyeglass lens grinding apparatus is known. After a subject lens is chucked by two lens rotating shafts, the apparatus controls the axis-to-axis distance between an axis of the lens rotating shafts and an axis of an abrasive wheel shaft of a grinding abrasive wheel on the basis of processing data while rotating the lens, thereby grinding the lens in pressure contact with the abrasive wheel. The apparatus of this type has a processing-completion detecting mechanism for detecting whether or not the entire periphery of the lens has been processed in accordance with processing data. In general, the mechanism is designed to detect, through a mechanical contact or using a sensor, whether the axis-to-axis distance between the lens rotating shafts and the abrasive wheel shaft has reached a predetermined distance based on the processing data.
In the case where the lens chucked by the two lens rotating shafts is processed by being brought into pressure contact with the abrasive wheel, the lens rotating shafts are slightly deflected due to their rigidity in a direction in which the lens rotating shafts escape from the abrasive wheel. The lens is clamped through a suction cup; however, if the rigidity of the suction cup portion is weak, the lens is also slightly deflected in the direction in which it escapes from the abrasive wheel. For this reason, the above-described processing-completion detecting mechanism determines the completion of processing at a stage where the actually ground lens is slightly larger than the intended size. This hinders the accurate processing.
As a conventional countermeasure against this problem, even after the completion of processing is detected, the lens is rotated idly until the deflection or distortion is overcome, to ensure that unprocessed portions will be processed.
However, if the number of idle rotations after detection of the completion of processing is set for the purpose of grinding all the lenses with high accuracy and such setting is made on the basis of thick lenses which are difficult to process, then excessive idle rotation (and thus wasteful processing time) is caused in the case of thin lenses even though the thin lenses have been already processed without any unprocessed portions. Conversely, if the setting of the number of idle rotations is insufficient (small), thick lenses cannot be processed with high accuracy.